1. Field
Embodiments relate to a light emitting device and more particularly, to a horizontal light emitting device with improved light extraction efficiency.
2. Background
Light emitting devices such as light emitting diodes or laser diodes using Group III-V or II-VI compound semiconductor materials implement light with a variety of colors such as red, green and ultraviolet light based on thin film growth techniques and development of device materials, implement white light with superior efficacy by using phosphor materials or combining two or more colors and have advantages such as low power consumption, semi-permanent lifespan, high response speed, safety and eco-friendliness, as compared to conventional light sources such as fluorescent lamps and incandescent lamps.
Accordingly, an application range of such a light emitting device has been expanded to transmission modules of optical communication systems, light emitting diodes as replacements for cold cathode fluorescent lamps (CCFLs) constituting backlights of display devices such as liquid crystal displays (LCDs), and white light emitting diode lighting devices as replacements for fluorescent lamps or incandescent lamps, vehicle headlights and traffic lights.
A light emitting device emits light having an energy determined by an inherent energy band of a material constituting an active layer (light emitting layer) upon recombination between electrons injected through a first conductive type semiconductor layer and holes injected through a second conductive type semiconductor layer. A light emitting device package emits light having a longer wavelength than light emitted from the active layer based on excitation of phosphors by light emitted from the light emitting device.
A great deal of research associated with light emitting diodes having a variety of structures is underway to improve luminous efficacy of light emitting devices. Research to improve light extraction efficiency of vertical light emitting devices by forming irregularities on surfaces of light emitting structures is underway and an attempt to improve light extraction efficiency of horizontal light emitting devices by forming a pattern on the surface of an insulating substrate is underway.
However, when irregularities are formed on a surface of an insulating substrate such as sapphire, the semiconductor layer constituting the light emitting structure is readily defected and may not be homogeneously grown due to lattice mismatch between the insulating substrate and the light emitting structure formed thereon, thus causing a decrease in luminous efficacy due to crystal defects present in the semiconductor layer.